1. Field of the Invention
The present invention relates generally to an apparatus for processing semiconductor wafers, and, more particularly, relates to a wafer boat assembly or the like within externally excited, chemical, reaction systems wherein the reactant material flows over the wafers or workpieces.
2. Description of the Related Art
Plasma enhanced chemical vapor reactors are known in the art. U.S. Pat. No. 4,799,451, for example, provides general background information about such systems and describes an improved boat assembly for use with such systems. Additional details regarding the operation of such systems are provided in U.S. Pat. Nos. 4,223,048 and 4,610,748. U.S. Pat. Nos. 4,223,048, 4,610,748, and 4,799,451 are incorporated herein by reference.
As is known to the art, such chemical vapor reactors operate by applying an external voltage to the boat assembly within a reactor tube to cause gasses within the reactor tube to form a plasma that is exposed to the surfaces of the semiconductor wafers positioned in the boat assembly. The operation of the reactors result in the deposition of a film of material onto the wafers. Conventional reactors have used a voltage source having a frequency of approximately 55 KHz; however, there are advantages to using a significantly higher frequency, such as, for example, 13.56 MHz. On the other hand, the use of the higher frequency has resulted in operational problems when the higher frequency is incorporated into existing systems. In particular, it has been found that the power from the external voltage source is not efficiently provided to the boat assembly As a result, the wafers in the boat assembly incur uneven deposition. In some cases, there is deposition of the film on the inner surfaces of the reactor tube, particularly in the vicinity of the electrical feedthroughs via which the high frequency voltage is brought into the tube and thus to the boat assembly. These are undesirable side effects of using the higher frequency voltage which outweigh the benefits for many users. Thus, a need exists to eliminate these side effects.